from moviepy import VideoFileClip, TextClip, CompositeVideoClip, concatenate_videoclips
text = TextClip("Hello, world!", font="Arial-Bold", fontsize=36, color="white")
video = VideoFileClip("video.mp4")
final_clip = CompositeVideoClip([video, text.set_pos(("center", "bottom"))])
final_clip.write_videofile("output.mp4")